Let's break this down. We're going to add 2488 and 8991 together.

Step 1: We'll start by adding the digits 8 & 1 in column 1 and get 9.

Step 2: We'll start by adding the digits 8 & 9 in column 2 and get 17.
We'll write down the last digit 7 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 4 & 9 in column 3 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 2 & 8 in column 4 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

So, 2488 + 8991 = 11479.

